Biomedical Engineering Reference
In-Depth Information
enzymatic hydrolysis of steam-exploded cornstalk in a membrane reactor coupled
with fermentation of acetone and butanol by
C. acetobutylicum
AS 1.132. A butanol
yield of 0.14 g
g
1
(cellulose plus hemicellulose) and maximum butanol productiv-
h
1
. The conversion
rates of cellulose and hemicellulose were 72 and 80 %, respectively.
h)
1
were obtained with a dilution rate of 0.075
ity of 0.31 g
(L
7.2.3
Continuous Fermentation and Immobilized Cell
Fermentation
The continuous cultivation technique can be used to improve reactor productiv-
ity and to study the physiology of the culture in a steady state. Reports have
indicated that continuous cultivation can be utilized with the same efficiency as
batch cultivation for solvent concentration and yield but with improved efficiency
regarding productivity. However, as a precaution of single-stage continuous pro-
cesses for the industrial scales, solvent production is not stable and declines
with time, with a concomitant increase in acid formation, although high solvent
yields can be achieved for various time periods. Fick et al. [
23
] maintained the
stable continuous cultivation of
Clostridium acetobutylicum
on a complex medium
containing 40 g
L
1
, but there
was less-efficient use of the substrate. Two- or multistage continuous fermentation
systems have been investigated in an attempt to separate the propagation phase
from the production stage. A laboratory-scale two-stage system was reported by
Bahl et al. [
24
]. A solvent concentration of 18.2 g
L
1
glucose for 2 months. The solvent yield was 13 g
L
1
L
1
(12.78 g
butanol) with
L
1
per hour was obtained
from
Clostridium acetobutylicum
DSM 1731 in a two-stage phosphate-limited
chemostate. The former Soviet Union in the 1960s [
25
] conducted multilevel
continuous fermentation (7-11 fermentation tanks) for solvent production. China in
the same period also carried out relevant research. The Shanghai Institute of Plant
Physiology and Ecology, Chinese Academy of Science [
26
], started the studies on
acetone butanol multilevel continuous fermentation, of which the solvent yield was
2.3 times higher than for batch fermentation.
Generally, the materials for immobilization of acetone butanol
Clostridium
cells
are absorbents such as clay brick, porcelain, and the like. Qureshi et al. [
27
,
28
] immobilized cells of
C. beijerinckii
onto clay brick particles by adsorption
and achieved a productivity of 15.8 g (L h)
1
. The use of immobilized cells
combined with advanced solvent recovery technologies for fed-batch or continuous
fermentation studies has also been carried out in recent years.
g
1
a yield of 0.34 g
and a productivity of 0.55 g
7.2.4
Solvent Recovery Process
Recently, some new online solvent recovery technologies have become available,
such as membrane-based systems, liquid-to-liquid extraction, adsorption, and gas
